A Comparison of Spectrophotometric

7/29/2019 A Comparison of Spectrophotometric

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A COMPARISON OF SPECTROPHOTOMETRIC AND GAS

CHROMATOGRAPHIC MEASUREMENTS OF HEAVY PETROLEUM

PRODUCTS IN SOIL SAMPLES

FARHAD NADIM1, SHILI LIU1, GEORGE E. HOAG1, JIANPING CHEN1,

ROBERT J. CARLEY1 and PETER ZACK21 University of Connecticut, The Environmental Research Institute, Longley Building, 270 Middle

Turnpike (Rte 44), Box U-5210, Storrs, CT, 06269, U.S.A.; 2 Connecticut Department of

Environmental Protection, Waste Bureau, Leaking Underground Storage Tank Program. 79 Elm

Street, Hartford, CT, 06106, U.S.A.

( author for correspondence, e-mail: [email protected])

(Received 18 August 1999; accepted 1 February 2001)

Abstract. Laboratory studies were conducted to compare the infrared spectrophotometry (TPH-IR)

and gas chromatography (TPH-GC) measurements of total petroleum hydrocarbon in soil samples.

Real world soil samples containing #2 to #6 fuel oils, mechanical lubricating oil, diesel fuel, ker-

osene, jet fuel and weathered gasoline were extracted with trichlorotrifluoroethane (Freon-113) and

methylene chloride. The extractants were analyzed using gas chromatography with flame ioniza-

tion detection (GC-FID) and infrared spectroscopy (TPH-IR) methods. A paired statistical t-test

was applied to compare the average of paired differences in the analytical results. Statistical tests

were evaluated with graphical presentation of the results. In general, a trend was observed in the

measured concentrations. Total petroleum hydrocarbon (TPH) concentrations measured with TPH-

IR had the highest readings. The same samples extracted with methylene chloride and analyzed with

GC-FID showed lower concentrations than the TPH-IR method while the GC-FID analysis of the

same samples extracted with Freon-113 produced the lowest concentrations. Laboratory experiments

indicated that TPH concentrations measured with the TPH-IR method were higher than the actual

quantities of petroleum hydrocarbon in the soil samples.

Keywords: freon-113, hydrocarbon contamination, petroleum product, statistical test

1. Introduction

Being a major industrial nation, the United States uses over 250 billion gallons

of oil and petroleum products each year on average. At every point in the oil

production, distribution and consumption process, oil is invariably stored in storage

tanks. The potential for an oil spill is high, and the effects of spilled oil often pose

threats to the environment. Leaking underground and aboveground storage tanks,

improper disposal of petroleum wastes, and accidental spills are major routes of

soil and groundwater contamination with petroleum products. In order to delineate

soil contamination and achieve regulatory cleanup levels, there is a need for accur-

ate determination of TPH concentration in soil samples. There are two common

practices for the measurement of TPH in soil samples: use of gas chromatography

with flame ionization detection (GC-FID) and the use of infrared spectroscopy

(TPH-IR).

Water, Air, and Soil Pollution 134: 97109, 2002.

2002 Kluwer Academic Publishers. Printed in the Netherlands.


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98 F. NADIM ET AL.

1.1. TPH MEASUREMENTS WITH GAS CHROMATOGRAPHY FLAME

IONIZATION DETECTION (GC-FID)

The use of gas chromatography is becoming a more commonly used method for

the determination of TPH in soil samples (Parr et al., 1996). Accordingly, theMassachusetts Department of Environmental Protection has set two categories for

the determination of petroleum hydrocarbon in soil and water samples. Volat-

ile Petroleum Hydrocarbon (VPH) Method covers gasoline-range volatile hydro-

carbons (C5 to C12). This method is based on a purge-and-trap, gas chromato-

graphy procedure. Photoionization detector (PID) and flame ionization detector

(FID) achieves detection. Extractable Petroleum Hydrocarbon (EPH) Method meas-

ures extractable hydrocarbons in soil and water samples with an approximate mo-

lecular weight range of C9 to C36. Samples are extracted with methylene chloride,

fractionated with silica gel to obtain an aliphatic fraction and a separate aromatic

fraction. The aliphatic fraction is analyzed by GC-FID to obtain C9-C18 and C19-

C36 aliphatic range data while the aromatic fraction is analyzed by PID to obtainC11-C22 aromatic hydrocarbon range and target polynuclear aromatic hydrocar-

bon (PAH) results. The precision of the measurements can be monitored with the

aid of surrogate standards (such as chloro-octadecane and ortho-terphenyl), internal

standards (such as 5-alpha-androstane), and matrix spike standard that is prepared

from five or more analytes from each analyte group independently from the cal-

ibration standards (Massachusetts-DEP, 1995). The GC-FID may be calibrated to

specified standards and has the ability to quantify industrial compounds. There are

less interferences with the GC-FID method and the analytical costs are less than

the TPH-IR method.

Compared to TPH-IR, TPH determination with GC-FID is a time consum-

ing procedure. Calibration of the GC instrument, preparation of the samples and

interpretation of the data requires tangible time and effort.

1.2. TPH MEASUREMENT WUTH TPH-IR (METHOD 418.1)

One of the common methods used for quantification of petroleum hydrocarbons

in soil and water samples is the EPA Method 418.1 (U.S. EPA, 1978; U.S. EPA,

1996b). A full review of the method and its limitations may be found in the works

of Sanford and Weston (1992), Bruce et al. (1995), and Parr et al. (1996). Method

418.1 is used for the detection of total petroleum hydrocarbon (TPH) in water

samples using infrared spectrometry. By substituting a soxhlet extraction procedure

for the separatory funnel procedure, this method may be modified and used for the

analysis of total petroleum hydrocarbon in solid matrices.

After the extraction of oil and grease from a sample, silica gel is added to the

extract to separate out the total petroleum hydrocarbons. Silica gel adsorbs the

polar material such as vegetable oils and animal fat. The method considers all oil

and grease materials that are not eliminated by silica gel adsorption as petroleum

hydrocarbons. Sodium sulfate is added to the sample during the extraction pro-


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SPECTROPHOTOMETRIC AND GAS CHROMATOGRAPHIC MEASUREMENTS 99

cedure and in the filtration process to eliminate any existing moisture in the sample

(U.S. EPA, 1995). Proper sample drying with sodium sulfate (or other drying agent)

prior to solvent addition is essential for good extraction efficiency.

An Infrared Spectrophotometer (TPH-IR) quantifies the extracted petroleum

hydrocarbon by measuring the concentration of C-H bonds and their bonding fre-

quency. The IR- absorbence of the extracted sample is measured at 3.41 m, and

then compared to the IR-absorbence of a known standard. According to the Beers

law within a certain limit there is a linear relationship between absorption and con-

centration. All compounds with carbon-hydrogen linkages have absorption bands

between 3.0 and 3.65 m wavelength due to C-H stretching vibrations. Benzenes

C-H absorption band at 3.3 m is strong and it is a unique band.

There are several limitations associated with the TPH-IR method that could

be outlined in the following categories. Compounds with high degree of volatility

are lost during analysis; with Freon-113 heavy hydrocarbon molecules (such as

hydrocarbon molecules found in #4 and #6 fuel oils) are not fully extracted; due to

the presence of strong oxidizers in some samples (such as samples with traces offertilizers) reduction of polar hydrocarbon to non-polar hydrocarbon causes high

and false TPH readings, and presence of suspended particles can be a problem

in some samples, but if the sample is properly filtered at the conclusion of the

extraction step they should not normally be a problem.

The TPH-IR method lacks analytical specification because the petroleum hydro-

carbons measured by the TPH-IR method are all compounds in the same sample

that are extractable with Freon-113, unabsorbed with silica gel and have IR-absorb-

ences at 3.41 m.

2. Study Objectives

In this study we compared the TPH-IR and GC-FID applications for the quantific-

ation of total petroleum hydrocarbons for different types of oil samples utilizing

an easily applicable statistical test. Laboratory studies were conducted to compare

the data obtained from TPH-IR and GC-FID-TPH for a widely used petroleum

based oils, such as #2 to #6 heating fuel oils, mechanical lubricating oil, diesel,

kerosene, jet fuel and weathered gasoline. The solvents used for this study were

methylene chloride and trichlorotrifluoroethane (Freon-113). Through this study

the extraction efficiencies of Freon-113 and methylene chloride for different grades

of fuel oil and their subsequent quantitation with an infrared analyzer (IR) and a

gas chromatograph were determined. Real world soil samples contaminated with

various petroleum products were extracted with Freon-113 and methylene chloride

(MeCl2) and were analyzed with a GC-FID and an IR-spectrophotometer. The

physical and chemical properties of heavy petroleum products used in this study

are given in Table I and the types of petroleum products in soil contaminants are

given in Table III.


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100 F. NADIM ET AL.

TABLE I

Some physical and chemical properties of petroleum products

Petroleum product Carbon range Specific gravity Boiling point range

Gasoline C6 C10 0.72 0.78 60 C 170 C

Diesel C8 C21 0.84 at 24 C 260 C 360 C

Kerosene C8 C16 0.83 at 15 C 190 C 260 C

Jet Fuel C8 C16 0.82 at 15 C 190 C 260 C

No. 2 C8 C21 0.84 at 24 C 260 C 360 C

No. 4 C8 C30 0.93 at 15 C Oil Specific

No. 6 C20 C78 0.95 at 15 C Oil Specific

Crankcase Oil C22 C50 Oil Specific Oil Specific

Lubricating Oil C20 C40 0.87 at 24 C Oil Specific

Light Crude Oil Oil Specific 0.80 at 24 C Oil Specific

IR-Reference Oil C6 C16 NA NA

From Woodruffet al. (1995), and Potter (1996).

3. Experimental Procedure

3.1. INSTRUMENTATION

A gas chromatograph Model HP-5890, Series II Plus was used for sample analysis.

HP-3365 Series II, Chem-Station version 8.03.34 and HP-GC ENVIROQUANT

G-1045A-8.00001 were used for quantitation of hydrocarbon compounds. The

column used was a capillary column, 30 m long, 0.53 mm ID, and film thickness

of 0.5 m (DB-1, J and W Scientific). The initial oven temperature was set at 40C for 2 min and raised to 290 C at 15 C min1, then held at 290 C for 10 min.

The detector temperature was set at 320 C. The total run time was 28.5 min. For

spectral analysis of the Freon extracted fuel, a MIRAN-1A infrared analyzer was

used.

3.2. CALIBRATION OF THE GAS CHROMATOGRAPHY

Based on USEPA Method-8015, the average response factor of n-alkane mixture

dissolved in isooctane was used to convert the total peak area of a sample chro-

matogram to TPH concentration. The straight chain alkane mixture contained C9

to C36 hydrocarbon components. The chromatography program was set to demon-

strate sufficient separation between the solvent and the first alkane peaks. The last

alkane component C36 eluted at about 27.5 min. C36 was used as the retention

time marker for oil identification. Samples were injected into the gas chromato-

graphy in a splitless mode through an automatic liquid sampler (HP Model 7673)


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at injection temperature of 290 C. The performance of the instrument was checked

with intermittent blanks, laboratory duplicates and calibration standards.

The average response factor of target analytes was calculated as follows:

Fi = Ai

Ci

Fa = (Fi)/n

%D = [(Fi Fa)/Fa] 100

Where:Ai = Response for individual n-alkane components in the sample, in total

peak area counts.

Fi = Response factor of an individual alkane

Ci = The mass (g) of alkane injected into the GC column

Fa = The average response factor of alkane standard, count g1

n = number of peaks

For initial calibration of the GC-FID, the n-alkane mixture was used at five

different concentrations (i.e., 50 g mL1, 100 g mL1, 200 g mL1, 500

g mL1 and 1000 g mL1). The concentration range of 50 g mL1 - 1000

g mL1 was used to fit into the working range of the detector and to cover the

expected range of concentrations found in real samples.

Based on USEPA Method-8015 and in order to check the linearity of the al-

kanes response factors by GC-FID, the average response factors of five GC-FID

injections of the straight chain alkane at five different concentrations (50 g mL1

1000 g mL1) were calculated and the results are tabulated in Table II. The

relative standard deviations (RSD = Standard Deviation/Fa) of the response factorswere calculated for each component of the straight chain alkane and the percent

RSD for all components were below 10%. The calibration results show that over the

concentration range of C9 to C36 petroleum hydrocarbon the GC-FID response is

linear. The tailing of the solvent peak may have caused the higher RSD for Nonane.

Concentration of TPH in soil samples was calculated as follows:

Concentration (gkg1) = [(Ax/Fa)(Vt/Vs)D]/W

Where:Ax = Response for the analyte in the sample, in total peak area counts.

Vt = Volume of extract, mL.

Vs = Volume of sample extracted, L.D = Dilution factor, if no dilution was made: D = 1 (dimensionless).

W = Weight of the extracted sample (kg). Depending upon the specific ap-

plication of the data the wet or dry weight may be used. The injection

volume of sample extract is the same as that of the calibration standard.


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102 F. NADIM ET AL.

TABLE II

Performance check of the GC-FID instrument and the linearity of alkanes

Alkane Average response factor Standard Relative standard

Fa Deviation (SD) Deviation

Nonane(9) 6464 541 8.4

Decane(10) 6858 113 1.6

Dodecane(12) 7010 113 1.6

Tetradecane(14) 6972 92 1.3

Hexadecane(16) 6951 89 1.3

Octadecane(18) 6908 55 0.8

Eicosane(20) 6888 34 0.5

Docosane(22) 6993 79 1.1

Tetracosane(24) 6664 160 2.4

Hexacosane(26) 6842 144 2.1

Octacosane(28) 7181 342 4.8

Triacontane(30) 6985 115 1.7

Dotriacontane(32) 7163 157 2.2

Tetratricontane(34) 6663 98 1.5

Hexatriacontane(36) 7017 81 1.2

RSD% = SD/Fa 100.

3.3. METHOD PERFORMANCE CHECK WITH GC-FID

Nineteen soil samples with sandy texture ( 10 g each) were taken from a site with

no history of petroleum hydrocarbon contamination. Sixteen samples were spikedwith a mixture of #2 oil, #6 oil, kerosene and motor oil (100 g of each). The total

mass of oil in the spiking solution was 400 g. Three soil samples were used as

controls. All soil samples were kept in jars with Teflon sealed caps for 48 hr in

room temperature of 24 C. Samples were then extracted with methylene chloride

using EPA Ultrasonic Extraction Method-3550 (U.S. EPA, 1995) and analyzed by

GC-FID. Each sample was extracted three times with approximately 10 mL of

MeCl2 and the extracts were placed in a 100-mL grade-A volumetric flask. By

adding MeCl2 to the flask the solvent level was brought up to the 100 mL marker.

The average recovery of all sixteen spiked samples was 103%. The standard de-

viation was 12% and the RSD value ranged from 11 to 20%. TPH levels in the

control samples were all below the detection limits of the GC-FID instrument.

3.4. DETECTION LIMITS

The method detection limit (MDL) may be defined as the minimum concentration

of a substance that can be measured and reported with 99% confidence that the


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Figure 1. Comparison of IR absorbences for different fuel oils and the reference oil.

value is above zero (U.S. CFR-40, 1998). Applying the method detection limit

(MDL) study, the method detection limit for the straight chain alkane and four

oil samples extracted from the sixteen soil samples were measured and the limits

ranged from 0.052 mg kg1 for #2 fuel oil to 0.714 mg kg1 for straight chain

alkanes.

3.5. CALIBRATION OF THE INFRARED SPECTROPHOTOMETER

Following EPA Method 8440 the standard solution was made by mixing 15 mL

n-hexadecane (C16), 15 mL isooctane (C8), and 10 mL of chlorobenzene (C6) as

the reference oil in a 50 mL glass stoppered bottle. Calibration of the TPH-IR

instrument was done by preparing five standards from the reference oil over the

concentration range of 25 mg L1 to 500 mg L1. Concentrations exceeding 500

mg L1 were beyond the detection range of the instrument.

3.6. METHOD PERFORMANCE CHECK WITH TPH-IR

The TPH-IR absorbences for different oils were measured and the results are shown

in Figure 1. Figure 1 indicates that as the concentration of the oil in Freon-113

increases the difference in IR-absorbences for different fuel grades becomes larger

(#6 oil and kerosene have the lowest and the highest absorbences respectively). Fig-

ure 1 shows that for all of the petroleum products used in this study, the reference

oil had the lowest response.


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104 F. NADIM ET AL.

3.7. SOIL EXTRACTION PROCEDURE

Eight soil samples were taken from the walls and bottom of excavation areas of

underground storage tanks used to store petroleum products. All soil samples had

a sandy texture with traces of silt and clay. Samples were numbered as sample-1

through sample-8. Samples 2,3,4,5,6, and 8 were collected from unsaturated soil

and samples 1 and 7 were taken from the region of subsurface that had periodically

been saturated with fluctuating groundwater table. Samples were extracted with

Freon-113 and methylene chloride. The extractants were analyzed with TPH-IR

and GC-FID. In order to calculate the concentration of petroleum hydrocarbon in

the soil samples, the IR instrument was calibrated with the reference oil that was

mentioned in the Calibration of the Infrared Spectrophotometer section.

Soil samples were extracted with ultrasonic extraction method (U.S. EPA Method-

3550, 1995). Approximately 10 g of soil was taken and thoroughly mixed with 10

g of anhydrous sodium sulfate inside a 100 mL (grade-A, Fisher Scientific) glass

beaker until it was like free flowing powder. Sonication was performed in specifiedpulse mode and the tip was positioned about 0.5 cm below the solvent surface

with a Fisher Sonic Dismembrator (Model-300) at 50% power for 3 min. Three

extractions were performed with each solvent. During the extraction procedure it

was observed that Freon-113 did not completely dissolve the #6 fuel oil. Methylene

chloride seemed to completely solubilize #6 fuel oil and this phenomenon was

clearly visible in the glass beakers used for extraction.

Extracting solvent was poured into a grade-A 100 mL volumetric flask through

a glass funnel that was packed with anhydrous sodium sulfate. For Freon-113 and

MeCl2 extractions, approximately three grams of silica gel (60200 mesh, David-

son Grade 950) was added to each sample extract in the 100 mL volumetric flask

to eliminate the non-petroleum oil. Mixtures were stirred for 5 min on a magnetic

stirrer.

4. Discussion

The MeCl2-extracted soil samples were analyzed with GC-FID and the Freon-113

extracts were analyzed with GC-FID and TPH-IR. Three 10 g portions of each soil

sample were taken and extracted in triplicate with Freon-113 and with methylene

chloride. In order to compare the results obtained from the analysis of the eight

soil sample extracts with methylene chloride and Freon-113, a paired statistical

t-test (95% confidence interval and 2 degrees of freedom) was used to compare

the average of paired differences. A paired statistical test is usually done when

two experiments are performed to independently make a series of tests (Lyman

1988; McBerthouex and Brown 1994). Instead of testing the null hypothesis that

states the difference in the mean of two samples is zero: a b = 0, we looked

at the problem in terms of the confidence interval of the average of differences.


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Figure 2. TPH concentration in soil samples measured with three independent methods. Error bars

represent one standard error of the mean values.

If the confidence interval of the average of differences included the value zero,then we concluded that there was no evidence in the data pointing at a statistically

significant difference between the two samples. Comparisons of the average values

are presented in Table III.

The concentration of TPH measured by TPH-IR had the highest value in all

samples except sample 1 and sample 7 where GC-FID measurements of methylene

chloride extracts were higher (Figure 2).

For soil samples contaminated with motor oil, statistical comparison of the

average of differences between GC-FID methylene chloride (MeCl2) extracts and

TPH-IR measurements do not indicate a significant difference between the two

analytical tests. Statistical tests done on soil samples 8 and 5 indicate that between

all analytical results there is a significant difference between all three methods of

measurements. The same test shows that there is no significant difference between

the GC-FID-Freon and TPH-IR measurements in soil sample 7.

Statistical comparison of TPH-IR and GC-FID-MeCl2 indicates that from eight

soil samples tested with the two methods, four samples show significantly higher

concentrations measured with the TPH-IR method. Comparison of TPH-IR and


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106 F. NADIM ET AL.

TABLE III

Statistical comparison of TPH concentrations in soil samples measured with three independent methods

Comparison of TPH-IR withGC-FID-MeCl2 Methods

Oil type Soil sample Upper level (CI) Lower level (CI) Test results

Motor Oil 1 0.06 1.02 No difference


Kerosene and HF6 3 3.49 0.17 Significantly highera

HF2b and HF6 4 11.43 5.43 Significantly higher

HF2 5 3.85 3.51 Significantly higher

HF2 6 2.25 0.02 No difference



Comparison of TPH-IR withGC-FID-freon methods

Oil type Soil sample Upper level (CI) Lower level (CI)c Test results

Motor Oil 1 1.92 0.28 Significantly higher


Kerosene and HF6 3 2.75 0.58 No difference

HF2 and HF6 4 10.69 5.16 Significantly higher





Comparison of GC-FID-MeCl2 with

GC-FID-Freon Methods

Oil type Soil sample Upper level (CI) Lower level (CI) Test results



Kerosene and HF6 3 1.97 4.12 No difference

HF2 and HF6 4 0.01 0.76 No difference


HF2 6 0.29 0.61 No difference



a Significantly higher means the results of the first method (according to the order noted in the table)

were significantly higher than the results of the second method.b HF2 is heating fuel #2 and HF6 is heating fuel #6.c CI = Confidence interval = 95%; /2 = 0.05/2 = 0.025, = (31) = 2 degrees of freedom and

t(,0.025) = 4.303.


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GC-FID-Freon extract measurements indicates that in six of eight samples, the

concentration of TPH measured with the TPH-IR method is significantly higher

than GC-FID-Freon and the other two samples do not show any significant dif-

ference in the measurements. Comparison of GC-FID-Freon and GC-FID-MeCl2

shows that for four samples, TPH concentrations measured with GC-FID-MeCl2are significantly higher than GC-FID-Freon-113 analysis.

For analytical measurements of TPH in the soil samples a trend is observed

that can be summarized as follows: TPH measurement of petroleum hydrocarbon

contaminated soils using Freon-113 extraction and subsequent TPH-IR measure-

ments show higher concentrations than methylene chloride extraction of same soil

samples analyzed with GC-FID, which in turn produces higher concentration read-

ings than Freon-113 extraction of the same soil samples analyzed with GC-FID.

One possible explanation for higher readings by TPH-IR may be that the Method-

418.1 reference oil was used to calibrate the TPH-IR instrumentation. Therefore the

TPH-IR analysis may have overestimated the petroleum hydrocarbon concentra-

tions to varying degree depending on the nature of the TPH concentration (Figure1). It was expected to see the TPH-IR results from samples 1,2,3 and 7 to also be

substantially higher than the GC-FID results (Figure 2). However, it is possible

that these samples had higher moisture content and were not thoroughly dried

using sodium sulfate. Therefore the Freon extraction efficiency was reduced far

enough to compensate for the over estimation inherent in the IR analysis with

418.1 reference oil calibration. It should be noted that drying of soil samples is a

critical step for accuracy and precision of both GC-FID and TPH-IR analysis of

soil samples (Crawford, 1999).

If the TPH-IR method is to be used as a tool for TPH measurements with Freon-

113 or with another solvent that is approved by U.S. EPA, comparative studies

must be conducted with other approved TPH methods to assure that false positivereadings are not produced with this method.

5. Conclusions

Total Petroleum Hydrocarbon (TPH) concentrations of soil samples taken from the

bottom and walls of excavated areas of former underground storage tanks storing

motor oil, kerosene, #2 and #6 fuel oil were quantified with TPH-IR and GC-FID

methods. The GC-FID method was applied for the methylene chloride (MeCl2) and

the trichlorotrifluoroethane (Freon-113) extracts. Therefore, three sets of quantit-

ative results were obtained for eight soil samples (i.e. TPH-IR, GC-FID-Freon and

GC-FID-MeCl2). Using a paired statistical t-test the average of paired differences

of the quantitative results were compared. Comparing the TPH-IR and the GC-FID-

MeCl2 methods indicated that TPH concentrations measured with TPH-IR method

were higher than the GC-FID-MeCl2 and GC-FID-Freon methods. Considering

the linearity of the alkanes response factors by GC-FID during calibration of the


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108 F. NADIM ET AL.

system and the performance check of the GC-FID instrument, it is very likely

that the TPH readings with the TPH-IR method were higher than the actual TPH

concentrations.

The GC-FID method could be more time consuming and may require more

efforts in preparation of samples than the TPH-IR method. Solvent extraction and

use of GC-FID can have a few advantages over the TPH-IR method. Petroleum

hydrocarbon compounds undergo physical and chemical processes in the subsur-

face and their initial mole fraction may change because weathering degrades the

lighter compounds. GC-FID chromatograms may be used to identify the nature and

sources of weathered hydrocarbon compounds in sites with history of petroleum

related contamination. The GC/FID performance can be checked through the use

of surrogates and standards. A gas chromatograph equipped with a flame ionization

detector (GC-FID) may be considered to be a suitable tool for TPH detection and

quantitation, due to the fact that most environmental laboratories use it for daily

sample analysis.

Due to the low extraction efficiency of Freon-113 for high molecular weighthydrocarbons, TPH-IR may be a suitable screening method for soils that are con-

taminated with lighter (C8 - C21) hydrocarbon compounds (such as diesel and no. 2

heating fuel). This method does not specify the class of petroleum hydrocarbon and

is highly sensitive to interference from non-hydrocarbon materials that naturally

exist in soil. Use of TPH-IR method would most often result in concentrations

higher than real values and the false positive readings could lead to extra and

unnecessary cleanup costs. The GC-FID can identify the source of hydrocarbon

contamination and errors associated with the method results are normally low and

controllable. Due to the ban on the production of Freon-113 in the United State,

EPA method 418.1 with application of Freon-113 as the extraction solvent may

not be practical anymore in the near future. If other solvents such as high-gradetetrachloroethylene are going to be substituted for Freon-113, the associated costs

of solvent purchasing and disposal should also be considered when comparing to a

GC-FID based TPH analysis.

Acknowledgments

The authors would like to thank the Waste Management Bureau of the State of

Connecticuts Department of Environmental Protection. Special thanks go to Mr.

Richard Crowley of the Environmental Research Institute for his laboratory as-

sistance and to two anonymous referees for their constructive comments on this

manuscript.


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Total Recoverable Petroleum Hydrocarbon, Method 418.1 (Spectrophotometric, Infrared). U.S.

Government Printing Office, Washington, DC.

Woodruff, E. B., Lammers, H. B. and Lammers, T. F.: 1998, Steam-Plant Operation, Seventh Edition,

McGraw-Hill Book Company, New York, 818 pp.

Documents

A Comparison of Spectrophotometric